Block 33a SP 13

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  • The steps in the pavement rehabilitation process apply to both HMA and PCC pavements.
  • These roads will need repair. Timing is everything. A surface treatment put on the road early is much less expensive and will extend the life of the pavement. The goal is to put together a maintenance and rehabilitation program that will be the most cost effective over the life of the pavement. An overlay placed before failure can result in a savings of over $200000 per mile.
  • Engineering economics procedures are used to analysis various alternatives. There are many alternatives to the maintenance and repair of a HMA pavement. The concept is to come up with a procedure that keeps the pavement condition high, the traffic disruption at a minimum and at the lowest life cycle cost.
  • HMA overlays are the most popular method of pavement rehabilitation. They provide a relatively fast, cost-effective means of correcting existing pavement deficiencies, restoring user satisfaction and adding structural capacity to the pavement structure. However, it is not uncommon for an HMA overlay to perform badly. The module should cover approximately three lectures. The first lecture would be introduction to HMA overlays, the second lecture would be structural overlays and the third would be HMA overlays over PCC pavements.
  • The purpose of a functional overlay is to provide a safe smooth riding surface to the traveling public. They are usually thin, (1 to 2 inch) and do not require extensive repair work prior to the overlay. The preparation prior to the overlay is minimal. It will consist of some crack sealing and maybe milling. A structural overlay is generally very thick and the preparation prior to the placement of the overlay can be extensive.
  • Where you would have only surface defects – a thin overlay or some type of surface treatment is appropriate – this would be a functional overlay. If there are structural problems with the pavement a thick overlay is required or possibly reconstruction.
  • A functional overlay is designed to deal with skid problems, ride deficiencies, etc. It is not used to correct a structural problem.
  • This slide shows a listing of the various functional problems that a thin functional overlay can correct.
  • If you have a friction problem it can be corrected by a thin overlay.
  • This photo shows polishing aggregate. The result is a very smooth, slippery surface.
  • The pavement show will present a hydroplanning problem. Note the water in the wheel paths. It appears that action is about to be taken to correct the problem. Note the milling machine. Typically the solution is to mill out the rutting layer and replace it with a new high stability HMA mixture.
  • Roughness can be caused by many things. It can be big bone jarring problems such as heaving or settlements or it can be raveling of the surface.
  • This shows a raveled pavement.
  • Generally functional overlays are thin layers and can consist of any or all of the items shown in this slide.
  • For many functional overlays the first step is to mill out the pavement.
  • There are a number of approaches to the development of the asphalt pavement thickness: 1. Engineering judgment – This approach us based on the experience of the design engineer. The engineer has been working in an area for many years and based on experience with past projects and the surface defects that are seen a thickness is chosen. 2. Deflection – The general concept is that the larger the deflection – the weaker the pavement is. Overlays can be used to strengthen the pavement structure to reduce the deflection to a desired level. Critical deflections can be determined below which the pavement is expected to perform satisfactory. 3. Structural deficiency – This approach uses the AASHTO design manual and makes assumptions about the structural coefficients for the layers of the existing pavement. The structural capacity of the existing pavement is determined and the needed structural capacity is determined. The difference between the two is the deficiency. 3. Mechanistic – Uses engineering mechanics and fundamental engineering properties . For overlay design it uses an engineering mechanics based simulation of the state of the stress and strain in the pavement to develop the design.
  • One of the most common ways of determining the properties of the asphalt pavement is to use deflection testing. A higher deflection results from a weaker pavement structure. The two distressess that are being addressed are the tensile stresses in the asphalt layers and the compressive stresses in the subgrade.
  • The typical surface deflection measuring equipment places an nondestructive test (NDT) load on the pavement and then sensors are used to measure the deflection. This data is used to compute the layer strengths.
  • A strong pavement will deflect less than a weak pavement. There are two things of interest – the amount of deflection and the steepness of the deflection basin.
  • This picture shows one model of deflection testing equipment.
  • If you have a structural problem – these are options to its correction. They range from a straight overlay to complete reconstruction.
  • As a part of the design process a number of things must be considered.
  • The amount of repair work done will affect the overlay thickness needed.
  • The next two slides shows different pavement distresses that may require preoverlay treatment. This slide shows rutting. It is necessary to consider the cause of the rutting problem and then correct it.
  • These cracks will reflect up through any overlay placed on the road. They need to be corrected – either by sealing or the section may need to be removed and replaced.
  • Block 33a SP 13

    1. 1. Rehab & Maint. HMA Overlays 1Flexible Pavement Maintenance andRehabilitationHMA OverlaysIntroduction and Functional OverlaysSenior/GraduateHMA Course
    2. 2. Rehab & Maint. HMA Overlays 2PavementDataCollectionProjectevaluationSelectfeasiblealternativesReconstructionRestorationRecyclingResurfacingLife - cyclecostsNon-monetaryfactorsSelectpreferredalternativesDetailedPS & EConstructionMonitorPerformanceSteps In The RehabilitationProcess
    3. 3. Rehab & Maint. HMA Overlays 3Rehabilitation FeasibilityPreventivemaintenanceSurface TreatmentThin OverlayReconstructionCritical conditionAGE or ESALThick OverlayPAVEMENT CONDITIONExcellentFailed
    4. 4. Rehab & Maint. HMA Overlays 4PavementConditionAlt.-AAlt.-BTerminal Serviceability IndexAnalysis PeriodAnalysis PeriodRSL
    5. 5. Rehab & Maint. HMA Overlays 5Covered in this module• HMA Overlays over HMA pavements– Functional– Structural• HMA Overlays over PCC pavements
    6. 6. Rehab & Maint. HMA Overlays 6Overlay Types• Functional overlays– Typically used to address surfacedistresses or improve ride quality– Generally not designed and rely on pastexperience• Structural overlays– Correct structural deficiencies and aredesigned using the methods presented(or other methods)
    7. 7. Rehab & Maint. HMA Overlays 7Thin Overlay Thick OverlaySurface Defects Structural DefectsSelection of an Overlay toCorrect Deficiencies
    8. 8. Rehab & Maint. HMA Overlays 8Functional Overlays• Remedy functional deficiencies• Minimum constructable thickness• May involve surface milling and repair withoverlay
    9. 9. Rehab & Maint. HMA Overlays 9Functional Deficiencies• Adversely affect highway user– Poor surface friction– Hydroplaning– Excess surface distortion• Rutting• Potholes• Faulting• Settlement
    10. 10. Rehab & Maint. HMA Overlays 10Surface Friction• Force developed at tire-pavementinterface that prevents sliding• Factor influencing– Microtexture– Macrotexture– Transverse slope• Poor friction can be caused by polishingor bleeding
    11. 11. Rehab & Maint. HMA Overlays 11Photo of poor surface friction
    12. 12. Rehab & Maint. HMA Overlays 12Hydroplaning• Tires ride on thin film of water and losecontact with the pavement• Hydroplaning is worsened by water standingon the pavement and is affected by thefollowing– Wheelpath rutting– Lack of surface texture– Lack of cross slope
    13. 13. Rehab & Maint. HMA Overlays 13Photo of rutting in wheelpaths
    14. 14. Rehab & Maint. HMA Overlays 14Structural OverlaysFlexible Pavement Maintenance andRehabilitation
    15. 15. Rehab & Maint. HMA Overlays 15Surface Roughness• Irregularities in the pavement surface that adverselyaffect ride quality, safety, and vehicle maintenancecosts• HMA Pavements– Heaves, settlements– Deteriorated cracks– Potholes– Raveling• PCC Pavements– Heaves, settlements– Spalling– Faulting– Curling/warping– Texture application
    16. 16. Rehab & Maint. HMA Overlays 16Photo of raveling
    17. 17. Rehab & Maint. HMA Overlays 17Options for Correcting FunctionalDeficiencies• Thin overlay - 50 to 80 mm (2 to 3 in)• Milling plus thin overlay• Open-graded friction course• Full-depth or partial-depth repairs• Thin, hot-applied surfacing
    18. 18. Rehab & Maint. HMA Overlays 18Photo of milling
    19. 19. Rehab & Maint. HMA Overlays 19Structural Deficiencies• Adversely affect the load-carrying capabilityof the pavement• Indicators– Cracking– Distortion (rutting)– Disintegration
    20. 20. Rehab & Maint. HMA Overlays 20Photo of alligator cracking
    21. 21. Rehab & Maint. HMA Overlays 21Thickness Design• Engineering judgment• Deflection• Layer deficiency• Mechanistic
    22. 22. Rehab & Maint. HMA Overlays 22Subgrade SoilBase/SubbaseSurface SURSUBSURAxleLoadPavement Deflections
    23. 23. Rehab & Maint. HMA Overlays 23NDT SensorsNDTLoadMeasurement of SurfaceDeflection
    24. 24. Rehab & Maint. HMA Overlays 24NDT Load“Strong”Pavement “Weak”PavementStrong vs. Weak Pavements
    25. 25. Rehab & Maint. HMA Overlays 25Dynatest FWDLoadDeflection measuringsensors
    26. 26. Rehab & Maint. HMA Overlays 26Options for Correcting StructuralDeficiencies• Structural overlay• Preoverlay repair and structural overlay• Recycling and structural overlay• ReconstructionAASHTO procedure provides an overlaythickness to correct a structural deficiency
    27. 27. Rehab & Maint. HMA Overlays 27Considerations for Overlays• Preoverlay repair• Overlay materials• Subdrainage• Reflection crack control• Traffic loadings• Pavement widening
    28. 28. Rehab & Maint. HMA Overlays 28Preoverlay Repairs• Amount and type depends on– Type of overlay– Structural adequacy– Distress types and severity– Future traffic loadings– Physical constraints– Overall project funding
    29. 29. Rehab & Maint. HMA Overlays 29Preoverlay Repairs• Consider trade-offs between– Overlay type– Overlay thickness– Preoverlay repair extent
    30. 30. Rehab & Maint. HMA Overlays 30
    31. 31. Rehab & Maint. HMA Overlays 31

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